GstValidate Scenario File Format

To be able to define a list of actions to execute on a GstPipeline, a dedicated file format is used. The name of the scenario is the name of the file without its .scenario extension. The scenario file format is based on the GstStructure serialized format which is a basic, type aware, key value format. It takes the type of the action in the first comma separated field, and then some key value pairs in the form parameter=value separated by commas. The values type will be guessed if not casted as in parameter=(string)value. You can force the type guessing system to actually know what type you want by giving it the right hints. For example to make sure the value is a double, you should add a decimal (ie. 1 will be considered as a int, but 1.0 will be considered as a double and "1.0" will be considered as a string).

For example to represent a seek action, you should add the following line in the .scenario file.

seek, playback-time=10.0, start=0.0, flags=accurate+flush

The files to be used as scenario should have a .scenario extension and should be placed either in $USER_DATA_DIR/gstreamer-1.0/validate/scenarios , $GST_DATADIR/gstreamer-1.0/validate/scenarios or in a path defined in the $GST_VALIDATE_SCENARIOS_PATH environment variable.

Each line in the .scenario file represent an action (you can also use \ at the end of a line write a single action on multiple lines). Usually you should start you scenario with a meta structure in order for the user to have more information about the scenario. It can contain a summary field which is a string explaining what the scenario does and then several info fields about the scenario. You can find more info about it running:

gst-validate-1.0 --inspect-action-type action_type_name

So a basic scenario file that will seek three times and stop would look like:

meta, summary="Seeks at 1.0 to 2.0 then at \
3.0 to 0.0 and then seeks at \
1.0 to 2.0 for 1.0 second (between 2.0 and 3.0).", \
seek=true, duration=5.0, min-media-duration=4.0
seek, playback-time=1.0, rate=1.0, start=2.0, flags=accurate+flush
seek, playback-time=3.0, rate=1.0, start=0.0, flags=accurate+flush
seek, playback-time=1.0, rate=1.0, start=2.0, stop=3.0, flags=accurate+flush

Many action types have been implemented to help users define their own scenarios. For example there are:

  • seek: Seeks into the stream.
  • play: Set the pipeline state to GST_STATE_PLAYING.
  • pause: Set the pipeline state to GST_STATE_PAUSED.
  • stop: Stop the execution of the pipeline.

NOTE: This action actually posts a GST_MESSAGE_REQUEST_STATE message requesting GST_STATE_NULL on the bus and the application should quit.

To get all the details about the registered action types, you can list them all with:

gst-validate-1.0 --inspect-action-type

and to include transcoding specific action types:

gst-validate-transcoding-1.0 --inspect-action-type

Many scenarios are distributed with gst-validate, you can list them all using:

gst-validate-1.0 --list-scenarios

You can find more information about the scenario implementation and action types in the GstValidateScenario section.

Default variables

Any action can use the default variables:

  • $(position): The current position in the pipeline as reported by gst_element_query_position()
  • $(duration): The current duration of the pipeline as reported by gst_element_query_duration()
  • $(TMPDIR): The default temporary directory as returned by g_get_tmp_dir.
  • $(SCENARIO_PATH): The path of the running scenario.
  • $(SCENARIO_DIR): The directory the running scenario is in.
  • $(SCENARIO_NAME): The name the running scenario

It is also possible to set variables in scenario with the set-vars action.

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